1. Field of the Invention
The present invention relates to an USB OTDR (Optical Time Domain Reflectometer) adapted to test fiber-optic connection status and more particularly, to such an USB OTDR, which uses USB port to provide power supply and to feed back test result to the computer and can be controlled by the computer to fetch related test data and result.
2. Description of the Related Art
A fiber-optic is a thin piece of fiber glass capable of transmitting light, having a diameter about 100˜150 microns, or slightly thicker than the hair. Therefore, a fiber-optic is light in weight and easily bendable. Using these features for communication by means of the application of light is called fiber-optic communication. Nowadays, fiber-optic communication has been practically used in our daily life. In fiber-optic communication, the fiber-optic acts the role that inputs data into a light beam for transmission. Therefore, a fiber-optic has an ingenuous internal structure that is made by a special technique. A fiber-optic is comprised of two parts, namely, the center part called the core, and the outer part called the clad. In order to transmit light ray, these two parts have different refractive indexes, and the refractive index of the core must be slightly greater than the clad. Thus, the major part of light entering the core causes a total reflection at the interface between the core and the clad so as to keep passing forwards, i.e., the light beam passing from the core toward the clad is totally reflected at the interface between the core and the clad and prohibited from passing to the outside of the clad. Even if the fiber-optic is curved, the light beam will be collided with and reflected by the interface between the core and the clad and will simultaneously keep passing forwards along the core of the curved fiber-optic.
Therefore, a fiber-optic has the following advantages:
1. Thin thickness: When one thousand pieces of fiber-optics arranged into a bundle, the width of the bundle of fiber optics is just about 7 cm.
2. High data transmission rate and long transmission distance: The transmission rate of a fiber-optic can be as high as 100 Gbps, and its transmission distance can be as long as 100 km. Functionally, one fiber-optic communication line is about equal to ten thousands of telecommunication lines.
3. Having a light weight and corrosion-proof and electric wave interference preventive characteristics, and being durable in use.
As stated above, a fiber-optic can be installed at a long distance. During installation, fusion splices and connectors are used to extend the distance of the fiber-optic, and there may be bend, fiber end, or other conditions that may cause poor optical communication. Conventional OTDRs are capable of detecting the aforesaid various conditions, and finding out fault-locating of fiber link.
FIG. 1 is a system block diagram of an OTDR according to the prior art. As illustrated, the OTDR comprises a front connector 10, a laser diode 11, a coupler 12, a pulse generator 13, an APD (avalanche photodiode) 14, an amplifier 15, an AD converter 16, control, signal and data processing 17 module, and a display 18.
The fiber-optic under test is connected to the front connector 10. After connection of the fiber-optic under test to the front connector 10, the control, signal and data processing 17 controls the pulse generator 13 to generate a pulse signal, causing the laser diode 11 to generate an optical signal. The optical signal from the laser diode 11 passes through the coupler 12 to the fiber-optic under test. If an abnormal condition occurred in the fiber optic under test, a feedback signal will be produced and monitored. The reflected signal from the fiber-optic under test will be received by the APD 14 via the coupler 12, and then amplified by the amplifier 15, and then converted into a digital signal by the AD converter 16, and then processed by the control, signal and data processing 17 module for output through the display 18.
FIG. 2 is an OTDR test result chart according to the prior art. As indicated in the waveform, the OTDR can search the distances (locations) of different line conditions including front connector 21, fusion splice 22, connector 23, bend 24, poor connector 25, backscatters 26, and fiber end 27. As indicated, the fiber-optic signal is attenuated with the distance, and different conditions produce different signals. Subject to signal attenuation status and signal produced, fault-locating fiber link is monitored, and maintenance or repair work can rapidly be performed subject to the test result.
Therefore, an OTDR is an important tool to offer an in-service fault-locating of fiber link in fiber-optic transmission systems. However, because conventional OTDRs are a combination of hardware and software, they are commonly heavy and bulky, not easy to move.
Further, USB (Universal Serial Bus) devices have been well developed and intensive used in any of a variety of electronic apparatus including mice, scanners, displays, printers, and etc. When using a certain peripheral apparatus, you need only a plug the USB plug of the peripheral apparatus to the USB socket of a computer of the USB hub of a computer network, and the computer will automatically detect the model of the newly installed peripheral apparatus and install the related driver. When not required, the user can disconnect the USB plug of the peripheral apparatus at anytime without affecting the operation of the window system of the computer. Except the aforesaid advantages, transmission speed of an USB device is more than ten times over a conventional parallel device. Further, it is not necessary to provide additional power cords for peripheral apparatus that are connected to an USB hub because the USB connector of every peripheral apparatus can be obtain the necessary working voltage through the USB hub. Therefore, the use of USB devices lessens the problem of the arrangement of power sockets.
Further, various mobile digital products such as notebook computers, PDAs (Personal Data Assistants) and etc. have been well developed and intensively used by people in every country. These products are commonly incorporated with USB connectors or the like. Combining an OTDR with these mobile digital products will greatly improve the convenience of the use of these mobile digital products.